Electron tube for generating high frequency oscillations



Odi- 7, 1958 J s. A. ToMNER ET AL 2,855,532v

ELECTRN TUBE FOR GENERATING HIGH FREQUENCY OSCILLATIONS Filed July 21, 1954 K 2 Sheets-Sheet 1 Oct. 7, 1958 J. s. A. TOMNER ETAL 2,855,532

, ELECTRON TUBE FOR GENERATING HIGH FREQUENCY OSCILLATIONS Filed July 21, 1954 2 Sheets-Sheet 2 Fg.3 I Fff) H95 1o 203'04'05'0 o o( Fig. 6

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ELECrRoN TUBE Eon GENERATNGHIGH FREQUENCY oscILLArloNs V.leanSigvard AgneTomner, Johanneshov, and Sven Gustaf. Gustafsson, Stockholm, I Swedelnyassgnors to Telefonaktiebolaget `L M Ericsson, Stockholm, Sweden, a corporation of Sweden Application July 21,1954, Serial No. 444,887

Claims priority,.application Sweden August 15, 1953 3 Claims. (Cl. 313-157) Thisninventionl relatesy to an electron tube `permeated by a magnetic field for generating high frequency oscilla-H tions and particularly a tube of this kind arrangedvfor variable tuning within a wide frequency range.

The principle of the electron tube to which the inventionrelates is described in the copending U. S. patent application of H. O. G. Alfven and Dag Rommell, Ser. No. 284,978, which is now abandoned. In such a tube the electrons, which are accelerated `in an electrostatic field parallel to the magnetic field, exchange energy with a high frequency electric field while oscillating to and fro. electronsa drift movement perpendicularvto the electrostatic field.

It is'known that the oscillation frequency of the tubes described in the above U. S. patent application 284,978

maybe varied by means of` varying the field strength of the electrostatic field causing the electrons to oscillate, i. e. the voltage of suitable electrodes.

This method for` tuning the tube has` however the following disadvantage. The' output power `of the tube will vary with the` frequency, and the voltage sources will be rather complicated. y y

The obj-ect of the inventionrv is chieiiyto improve electron tubes of lthe above described kind, tomake them. better suited for generating .frequency modulated oscillations having a great frequency deviationwan'd vgood linearity.

The invention relates especially toa further .development of the coaxial tube shown in said U. S. patent application Ser. No. 284,978, Figs. 7a and 7b, said coaxial tube being united With a Wave guide,.a tubular part of which serves as reflector electrode, and the lanode being located centrally in said part of the vwave g-uide.`

The above described electron tube, the discharge space,

having a component directed perpendicularly to the `mag-v netic field but in the same plane thereof, which com. ponent imparts a drift movementto Ltheelectrons per,- pendicular to said field and said component.

The electron tube according to the invention ischaracterized by means `being provided4 for turning thel tubel around its axis, *which is perpendicular to the field` lines of the magnetic field, whereby'thev oscillation frequency of the electrons and thus the frequency ofthe generated high frequency oscillations Willnbe changed without the electrode potentials being changed.

The tube comprises .means to impart to the lCe The invention will be closer described with reference l type shown in U. S. patent application Ser. No.'284,978.V

connected to a tuned circuit,

Fig. 7 shows the electrode system of a tube according to the invention, connected to a tuned circuit.

The tube shown in Figs. 1 and 2 comprises withinvan envelope 40 a cathode 1, located in an ,aperture in a -tubefshaped reflector electrode 4 yand a cylindrical anode 2. The inner surface of the reflector electrode 4 and the anode 2 define an elongated discharge space. At the upper vend of this discharge space, as shown in Fig.y l a Vcollector electrode 7 is arranged, while cathode 1 is located at the opposite end of the discharge space. The cathode 1 is so arranged, that a diameter through the cathode forms an angle a with a diameter perpendicup lar tothe magnetic field, as is shown in Fig. 2. The. cathode1which is supported bythe cathode leads .45, is manufactured of tantalum, tungsten or thorated tungsten, and it is spiralizedin the usual manner to increase the emitting surface Without increasing the heater. current required. tured of tantalum, whereby a gas absorbing getteraction isobtained and a special getter may be avoided.` The anode. is` cylindrical, as a round anode gives an alrnost` parabolicvoltage distribution if the rest ofthe electrode systemfis suitably shaped, as is seen. from Fig.,4 yof the. above` mentioned U. S. patent application. Ser. No.' 2%4978..` l v The shown.,electrode system with a cylindrical anode coaxially located Within a tube-shaped reflector electrode. gives an electrostatic field, the voltage distribution of which in a segment plane through ,the cathode, parallel with the magnetic field, is approximately parabolic for different values of a. rl`he parabolic voltage distribu-v tion .has the effect, that the oscillation frequency of the electrons will be independent of the oscillation amplitude provided that the electrons .pass the same maximuml provided with a collar 43, which surrounds the upper ends ofthe anode 2 and the reflector 4. The `collectoi is surrounded by a sleeve 41 of Kovar, which is sealed ybetween the envelope 40 and an upper` portion 40a of 'saidenvelope, but is chiefly free fromthe collector itself,\so` that at the centre of saidcollector, where the glass seal to the envelope 40 is located, a circular space 42 is formed. Thus, the copper collector need not be vacuum tightened towards the sleeve 41, which is an advantage with regard to the different heat expansion coefficients' of these materials. The sleeve 41 may be provided with1 cooling flanges (not shown on the drawing) for increasf ing the heat removal from Athe collector7, which is strongly heated during the operation of the tube.

The reflector electrode 4 is at its lower end prolonged by a sleeve 101, for example of Kovar, which is provided.

Withfaii insulating tube 103, forlexamp'le o'fuTeJlosaidfl sleeve being inserted in a coaxial outer Acondu'ctc`i105,"`

Patented Oct..7, 1$5

The anode 2 Vis preferably manufac-v and the tube 101 is supported by the insulating sleeve 103, whereby the envelope 40 can be rotated in relation to the coaxial line 104, S. The whole tube can be rotated by turning the handle 46 but for facilitating a precise adjustment ofthe angle a, shown in Fig. 2, the tube may be rotated by means of any suitable lever or gear mechanism. By providing the upper part of the inner and outer conductors 104 and 105 of the coaxial line with an axial slit, the bearing will be resilient, whereby the tube 40 will remain in a selected position after adjustment.

The magnetic eld is obtained from a permanent magnet 47, which is shown in Fig. 2 but not in Fig. 1. The pole pieces of this magnet are so high, that a fairly homogeneous field is obtained in the elongated discharge space. Suitably, the height of the pole pieces is made equal to the diameter of the envelope 40, and the lower part of the magnet is placed at the same level as the cathode.

When the tube is operating and under the influence of the outer magnetic iield (indicated by B in Figs. 3 and 4) permeating the discharge space, the electrons emitted by the cathode 1 have an oscillatory movement as shown in Figs. 3 and 4, whilst they are imparted a drift movement upwards under the influence of that component of the electrostatic field perpendicular to the magnetic tield between the reflector electrode 4 and the anode 2. When the oscillating amplitudes of the electrons have fallen to a fraction of the original amplitude, they hit the collector `7. The generated high frequency oscillations are taken out from the coaxial system104, 105 by means of a probe located in a holder 107 on the outer conductor 105, and their frequency can be adjusted by displacing the tuning means indicated by 108 and provided with a short-circuiting device 102.

Figs. 3 and 4 schematically show sections through the electrode system in a tube according to the invention and their object is to illustrate how the tube, by partial rotation about its axis relative to the magnetic field B, can be operated at different frequencies with the same anodeand reflector voltages. As is stated in the said U. S. patent application Ser. No. 284,978, the following expression is valid for the oscillation frequency of the electrons:

1/2 f co nstantY- d being the oscillation amplitude of the electrons and V the highest potential passed by the electrons. In Figs. 3 and 4 the cathode, the anode and the reflector electrodes are indicated by 1, 2 and 4. a and b are the radius ofthe anode and respectively the reflector electrode. V1 and V2 indicate the 'maximal potential passed by the electrons, d1 and d2 their oscillating amplitude, and a1 and a2 the angle between a line from the cathode 1 to the middle of the anode and a vertical reference plane through said middle. By turning the tube an angle er1- a2 the case shown in Fig, 4 is obtained. A comparison between the Figs. 3 and 4 shows, that such a turning of the tube round its axis, which axis goes through the middle ofthe anode, changes the maximal potential passed by the electrons from the value V1 to the value V2 and the oscillating amplitude of the electrons from the value d1 to the value d2. The oscillation frequency can be' expressed in the following manner:

f= constant b sin a Vd'being the voltage difference between the anode 2 and the cathode 1. In Fig. 5, the function F(m)=[1n(b/ 1.eos 51)]1/2 S111 a has been drawn for a value b/ a=2.

Supposing that the tube is operated at a certain frequencyf; and the coaxial resonator is tuned to said frequency, the potential difference Vd between the anode and the cathode and the potential of the rellector electrode, which is negative in relation to the cathode, must then be so adjusted, that the right oscillation frequency is obtained for the electrons. If the setting of the shortcircuiting device 102 (Fig. l) is changed so that the coaxial conductor is tuned to a higher frequency f2, it is evidently not necessary to change the potential of the different electrodes in order to affect the oscillation frequency of the electrons, but it is only necessary to turn the tube round its axis in the manner shown in Figs. 3 and 4, keeping the said potentials constant. To be able to cover a frequency range of for example 1400-2000 mc./s. in an electric tube made according to the said patent application it is usually necessary to vary the voltage Vd from 1000 to 2000 volts. By varying instead the turning angle a according to the invention, the tube can be operated over its whole tuning range with a negligible change of the applied voltages. The tube according to the invention obviously presents a considerable advantage over the known tube.

The object of Figs. 6 and 7 is to show the difference between the oscillation mode in a tube according to the fundamental embodiment in the U. S. patent application Ser. No. 284,978, shown in Fig. 6, and a tube according to the invention, shown in Fig. 7. ln these Figures 1, 2, 4, 4 represent the cathode, the anode and respectively tbc reflector electrodes. 126 is the source of anode potential, 125 the outer resonance circuit and 127 the oscillation plane of the electrons between the reflector electrodes 4, 4 and respectively within the reflector electrode 4.

A proper phase relation between the oscillating electrous and the high frequency oscillations requires that the transit time from one of the reflector electrodes 4 to the anode 2 in the known tube corresponds to a quarter of a period, whereas in the tube according to the invention it must correspond to a half period. At a given anode voltage and electrode spacing the tube according to the invention will thus oscillate with double the frequency, compared to the known tube. Since the oscillation frequency of the electrons is proportional to the square root of the anode'voltage according to the above given formulae, the difference between said two types of tubes can be described so, that for the same frequency and electrode interval the anode voltage of the tube according to the invention is a quarter of the anode voltage of the known tube.

Different modifications of the shown embodiment may be made without the spirit of the invention being departed from.

We claim:

1. An electron tube, the discharge space of which is permeated by a magnetic field, and in which eiectrons accelerated in an electrostatic field parallel to the magnetic field exchange energy with a high frequency electric lield while oscillating to and fro, said tube comprising at least one cathode, one anode, one cylindric reflector electrode and one collector, with the anode located centrally in the discharge space limited by the reflector electrode, the collector being placed at one end of said space and the cathode at the other end, the electric field arising between the reflector electrode and the anode having a component parallel to the magnetic field causing the electrons to oscillate to and fro along a chord parallel to the magnetic field and the electric field having a component directed perpendicularly to the magnetic field, said last nientioned component imparting to the electrons a drift movement perpendicular to said field land said first component, and means for adjusting the relative position of the tube and the magnetic field about the reiiector axis, whereby the oscillation frequency of the electrons, i. e. the generated high frequency oscillations can be varied withoutV changing the electrode potentials.

2. A high frequency generator comprising an electron tube having a tubular reflector electrode, a cylindrical anode located within said reector electrode, thereby forming an elongated annular discharge space between the reector and the anode, an electron emitting cathode located at one end of said discharge space adjacent to the reflector electrode, a collector electrode located at the other end of said discharge space, means for creating a magnetic field directed perpendicularly to the axis of said tubular reflector electrode, the component of the electric field between the reflector electrode and the anode parallel to the magnetic i'ield causing the emitted electrons to oscillate to and fro along a chord of the reliector electrode parallel to the magnetic eld, the component of the electric eld between the reflector electrode and the anode perpendicular to the magnetic eld causing the oscillating electrons to move slowly along the axis of the retiector elect-rode from the cathode to the collector electrode, and means for varying the angle seen in a plane perpendicular to the `axis of the reflector electrodes between a line through the center of the tubular reflector electrode and the cathode, and the magnetic lines of force, whereby the length of the chord along which the electrons oscillate, and, thus, the oscillation frequency is varied.

3. An electron tube having an evacuated envelope, a cylindrical anode extending from one end of the envelope toward the other, a rellector electrode coaXially surrounding and spaced from the anode, a collector electrode at the opposite end of the envelope substantially closing the space within the reector electrode, a concentrated cathode electrode in the reector electrode `adjacent the wall thereof at the end opposite the collector electrode, means directing a magnetic lield across the discharge space within the reflector perpendicular to the anode axis whereby it is parallel to a component of the electrostatic field extending from the reector electrode to the anode, said component imparting to and fro oscillations along a reector chord to electrons accelerated in the electrostatic lield parallel to the magnetic field, a component of the electrostatic ield normal to the magnetic eld imparting a drift movement to the electrons perpendicular to the electrostatic field and toward said collector electrode, means comprising a tuned coaxial line connected to the reflector and anode forming the oscillation circuit therefor, and means for relatively rotating the tube and magnetic field about the axis of the anode whereby the generated high frequency oscillations may be varied in frequency without changing the electrode potential.

References Cited in the tile of this patent UNITED STATES PATENTS 2,158,114 Fritz May 16, 1939 2,221,743 Wagner Nov. 12, 1940 2,395,647 Strobel Feb. 26, 1946 2,522,209 Cobine Sept. 12, 1950 2,768,328 Pierce Oct. 23, 1956 

